The turbomachine such as the centrifugal pump and so forth is mainly provided with a rotor having an impeller, a bearing which rotatably supports the rotor, a casing which contains therein the rotor and forms a stationary flow passage and so forth. In addition, the impeller imparts a dynamic pressure to the working fluid by rotating the rotor, converts the dynamic pressure into a static pressure at a part on the stationary flow passage which is formed in the casing, and thereby feeds the high-pressure working fluid under pressure to a demander and so forth.
Part of the working fluid which has been sucked into the turbomachine leaks through a gap part between the casing and the rotor. In order to reduce this leakage flow, the shaft sealing device is installed in the gap part between the casing and the rotor.
In a case of the centrifugal pump acting as the turbomachine which handles the liquid as the working fluid, in the centrifugal pump which is described, for example, in Japanese Unexamined Patent Application Publication No. Hei 10-259799 (Patent Literature 1), a so-called labyrinth shaft sealing device that labyrinth grooving has been performed on an inner circumferential surface on the casing (stator) side is provided for the purpose of preventing the working fluid from leaking to the outside through the gap part.
In the labyrinth shaft sealing device which is described in this Japanese Unexamined Patent Application Publication No. Hei 10-259799, a groove part (a circumferential groove) which is arranged in a circumferential direction and whose gap formed together with the impeller side becomes larger and a land part which is arranged in the circumferential direction and whose gap formed together with the impeller becomes smaller are alternately arranged in an axial direction and the leakage flow is reduced by utilizing an energy loss of a flow caused by abrupt expansion of a gap flow passage in the groove part and an energy loss of the flow caused by viscous friction on the land part as shown in FIG. 9 thereof. In addition, a width (a length in the axial direction) of the land part and a width (a length in the axial direction) of the groove part are configured to be almost the same as each other.
Incidentally, in a centrifugal compressor which handles a gas as the working fluid, for example, as indicated in Japanese Unexamined Patent Application Publication No. 2014-74360 (Patent Literature 2), use of a labyrinth seal (a pocket damper shaft sealing device) that a plurality of grooves have been formed in the axial direction and a plurality of pockets have been formed in a circumferential direction of each of the grooves is described (see FIG. 2 and FIG. 3 in Japanese Unexamined Patent Application Publication No. 2014-74360). In addition, it is described in this Japanese Unexamined Patent Application Publication No. 2014-74360 that in the labyrinth seal, simultaneous attainment of a reduction in leakage of the gas through a seal portion of the centrifugal compressor and improvement of damping characteristics at the seal portion is promoted.